Free wing aircraft may be used in STOL/VTOL applications where short landing and take-off distances are required. Free wing aircraft are relatively immune to turbulence and the like and also may provide high lift and good anti-stall characteristics since the free wing is generally free to pivot or rotate about its spanwise axis and thereby prevent excessive wind loading. As used in this present specification, a free wing or "freewing" is a wing attached to an aircraft fuselage in a manner such that the wing is freely pivotable about its spanwise axis preferably forward of its aerodynamic center. This arrangement enables the wing to have an angle of attack which is determined solely by aerodynamic forces acting on the wing. Rotation of the wing, without pilot intervention, induced by changes in the direction of relative wind over the wing surfaces, causes the angle of incidence between the wing and the aircraft fuselage to vary so that the wing presents a substantially constant angle of attack to the relative wind which, in horizontal flight, enable the aircraft to have such STOL free characteristics.
The aforesaid characteristics make the free wing particularly useful for STOL/VTOL aircraft, particularly for remotely piloted vehicles (RPV's) or unmanned aerial vehicles (UAV's). The stability of the free wing makes it an ideal aerial platform for instrumentation mounts (e.g., video camera, infrared sensor or the like).
Various technologies involving the use of a freewing in an aircraft having STOL and/or VTOL characteristics have been developed by the assignee of the present invention. One such technology is disclosed and claimed in prior application Ser. No. 07/850,913, filed Mar. 13, 1992, entitled "VTOL Free Wing Aircraft," wherein FIG. 1 therein (the relevant drawing figure and related disclosure of which is incorporated by reference herein in its entirety) depicts a STOL/VTOL free wing aircraft comprising a fuselage, a tail section, and a free wing with a propulsion system including an engine at the forward end of the fuselage for driving a propeller. The free wing is free to rotate or pivot about its spanwise axis and includes left and right wings extending from opposite sides of the fuselage. These wings are coupled together to collectively freely pivot about the spanwise axis. The aircraft therein further includes rudders and elevators in a tail section of the fuselage which may be controlled in a conventional manner for yaw and pitch control, respectively.
The operation of the VTOL free wing aircraft disclosed therein is as follows. At launch, the aircraft is mounted in a vertical orientation such as on a rail system which may comprise simply a guide or a track, and complementary guide or track following members on the aircraft for guiding the aircraft from vertical movement for a limited initial predetermined distance at lift-off. With the engine started and propeller backwash providing an air flow over the wings, the aircraft lifts off the launch rail. Catapult assist may also be provided. Yaw and pitch controls are maintained by the rudder and elevator, respectively. The air flow over the wings provides dynamic forces on the wings to control the roll of the aircraft during launch. The wings and launch are freely rotatable and the dynamic pressure on all control surfaces as a result of backwash from the propulsion system is intended to allow roll, pitch and yaw control over the aircraft during the initial phases of vertical launch.
To transition from vertical or horizontal flight, the pilot, computer or remote controller gives a downward elevator signal, causing the fuselage to pitch towards a horizontal orientation. By pitching the fuselage, the thrust vector also inclines from the vertical and thus has a horizontal thrust component. As the fuselage pitches toward the horizontal, the horizontal speed of the aircraft increases, causing the freely rotatable wing to rotate relative to the fuselage in accordance with the relative wind. The effects of the relative wind acting on the freely rotating wing quickly overcome the effects of the air flow over the wings from the propulsion system and, with increasing horizontal speed, the wing develops lift. The aircraft soon transitions into horizontal flight in a free wing flight mode.
To transition from horizontal to vertical flight, such as during landing, the reverse procedure is employed. That is, an up elevator command is given to rotate the fuselage toward a vertical orientation with its nose pointed upwardly. Horizontal speed is thus decreased and a vertical thrust vector is introduced. Accordingly, the relative wind changes and the thrust line and fuselage ultimately both rotate into a vertical or near vertical orientation. If the aircraft resists slowing and does not reduce its forward or horizontal speed sufficiently, the fuselage, by operation of the elevator, could be rotated past vertical so that the thrust line possibly serves as a thrust reverser, slowing the aircraft past STOL. Other slowing means are also possible.
In this embodiment, since the tail section is fixed to the fuselage and thereby immovable relative to the longitudinal axis and the thrust axis of the fuselage, relatively sophisticated recovery systems are necessary, such as extremely long and complex landing gear extending downwardly below the tail section in the vertical or near vertical flight landing mode as would be necessary for STOL and VTOL operations. This type of landing gear (e.g., a so-called moon rocket landing gear) would be extremely expensive and effective for use only on substantially level terrain.
Another free wing aircraft having thrust vectoring characteristics for propelling the aircraft in a horizontal flight mode and in a short field take-off and landing (STOL) flight mode is disclosed in the aforementioned '130 patent application. Therein, a fuselage including a source of propulsion is formed with a tail boom connected to extend rearwardly from the fuselage. The tail boom is formed with horizontal tail surfaces and vertical tail surfaces to provide for directional stability and yaw control. A mechanism is provided for relatively rotating the fuselage relative to the tail boom about an axis of rotation extending parallel to or coincident with the spanwise axis. This relatively rotating mechanism is operable to position the thrust line of the fuselage into an angle approaching, or of, 90.degree. relative to a longitudinal axis of the tail boom to enable the thrust of the propulsion system to propel the aircraft in the STOL flight mode.
The latter embodiment enables the use of less expensive and more practical, shorter types of landing gear wheel assemblies in comparison with the much longer landing gears required for the first described VTOL/STOL aircraft. Unfortunately, however, the use of landing wheels in the aforementioned STOL free wing aircraft formed with the articulated tail boom does not ensure that the aircraft will be capable of coming to a reliable stop such as when attempting to land in a comparatively confined space as for example on a ship's deck or a floating oil platform. Since the use of the aforementioned free wing aircraft have particularly promising applications when employed in an RPV or UAV type of free wing aircraft which must be recovered on such floating platform environments, it would be particularly desirable to provide a free wing aircraft having vertical and/or short take-off and landing capabilities (STOL/VTOL) without requiring either complicated land-based recovery systems or aircraft based wheel systems.
It is accordingly one object of the present invention to land an aircraft having vertical and/or short take-off and landing capability (STOL/VTOL) without requiring complicated land-based recovery systems for aircraft-based wheel landing systems.
Another object of the invention is to land free wing aircraft having STOL or VTOL capabilities in a confined space such as a ship deck without requiring complex and expensive arrestment systems or wheel-based systems.